As pointed out in my copending application Ser. No. 804,733, filed June 8, 1977, now U.S. Pat. No. 4,113,415, patented Sept. 9, 1978, an assembly of adsorbent-containing, alternately filtering dual filter units individually alternating between filtering and regenerating cycles, can dispense with drawing filtered gas for reverse-flow regenerating of the adsorbent from a purge tank or other compressed gas reservoir and use instead for the regenerating, part of the filtered gas from the filtering unit. The assembly disclosed in that application diverts part of the filtered gas from the filtering unit for regenerating the adsorbent in the other unit through piping connecting the filtered gas outlets of the two units and having in each unit a check valve for passing gas freely therefrom and a restricted orifice for discharging thereinto filtered gas from the other unit. As disclosed in Kreuter U.S. Pat. No. 3,324,631, the prior art had also recognized that possibility of utilizing part of the filtered air output of one of a pair of adsorbent-containing filter units for cyclically regenerating the adsorbent in the other filter unit by connecting the filtered air outlets of the two units through a passage restricted intermediate its ends by a single variable restrictor common to both units. In the Frantz application, the purpose of the restricted orifice in each unit is, by discharging the regenerating gas onto the downstream end of the adsorbent and at the same time restricting the discharge, to cause the gas to expand and consequently cool on issuing from the restricted orifice and thus both cool and regenerate the adsorbent. As opposed, the only purpose apparent from the Kreuter patent in the variable restrictor in the regenerating gas passage between the filtered gas outlets of the two units is to regulate the portion of the filtered gas output of the filtering unit diverted for regenerating the adsorbent in the other unit. It is to an improvement on the regenerating gas connection of filtered gas outlets of dual filter units that the present invention is particularly directed.